Robert W. Logan

Age- and Dietary-Related Distributions of Hepatic Arachidonic and Docosahexaenoic Acid in Early Infancy

ABSTRACT: A dietary-related deficiency of docosahexaenoic acid [C22:6(n-3)] in infant cerebral cortex has been identified. Absence or very low rates of hepatic synthesis from the essential fatty acid precursor, α-linolenic acid [C18:3(n-3)], in early life may have been a contributory factor. We have analyzed liver total lipid fatty acid compositions in 27 term (37–42 wk gestation) and 4 preterm (30–33 wk gestation) infants who died within the first 6 mo of life from sudden infant death syndrome. The infants were fed exclusively either human or formula milks. Formula-fed infants were subdivided into two groups, one receiving SMA milk with an α-linolenic acid content at 1.5% of total fatty acids and the other a composite group fed milks with low α-linolenic acid concentrations (<0.1% to 0.4%). The hepatic content of arachidonic acid [C20:4(n-6)] and docosahexaenoic acid was generally lower in both formula-fed groups than in the human milk-fed group. The age-related distributions of docosahexaenoic acid showed that coincident minimum levels were present in both formula groups in the third month of life. This may indicate that the hepatic enzymes involved in the final stage (A4-desaturation) conversion of α-linolenic acid to docosahexaenoic acid could be inactive in the first months of life. Emphasis must be on provision of preformed dietary docosahexaenoic acid and possibly arachidonic acid as well as their essential fatty acid precursors, to both term and preterm infants for at least the first 16 wk of life.

Transcutaneous iodine absorption in infants undergoing cardiac operation

Povidone-iodine is an effective antiseptic, but its topical use has been associated with a number of adverse reactions in burn patients and in neonates as a result of transcutaneous absorption. In particular, high plasma iodine concentrations are known to cause renal failure, metabolic acidosis, and thyroid suppression. Because of the permeable nature of the skin in small infants and the large areas cleaned before cardiac operations, it is possible that significant transcutaneous iodine absorption might occur in this situation. We have studied 17 infants, less than 3 months of age, who were undergoing closed cardiac or thoracic procedures. After povidone-iodine skin preparation in 15 (covering 20% to 30% of body surface area), plasma total iodine concentrations rose fourfold (range, 160% to 1,440%). This increase was significantly different from the preoperative level at 6, 12, 18, and 24 hours. There was no increase in plasma iodine concentration in 2 patients who were not exposed to povidone-iodine or any other iodine-containing compound. We discuss the implications for a topical antisepsis policy in infants.

HPLC of phospholipids in biological fluids — application to amniotic fluid for the prediction of fetal lung maturity

Because of both the advantage of speed compared with thin layer chromatography (TLC) and the dearth of high pressure liquid chromatography (HPLC) methods for phospholipid separation, it was decided to investigate the use of HPLC with a differential refractometer as detector for the separation and quantitation of amniotic fluid phospholipids required for the prediction of fetal lung maturity. A method was devised which gave results which compared well with those from TLC both in terms of quantitation and predictive value. Despite this, the method was found to lack sufficient reliability for application to the routine clinical assessment of fetal lung maturity. The method does, however, offer a good alternative to two dimensional TLC with phosphate analysis in research work involving quantitation of phosphatidyl inositol, phosphatidyl glycerol and particularly lecithin.

Assessment of the AmnioStat-FLM immunoagglutination test for phosphatidylglycerol in amniotic fluid.

One hundred and eight amniotic fluids were assayed by the AmnioStat-FLM (A-FLM) immunological agglutination test for phosphatidylglycerol (PG) and simultaneously measured enzymatically for PG content. Of 52 amniotic fluids found to be PG negative by the A-FLM method, all had enzymatic PG concentrations less than or equal to 1.5 mumol/l. Conversely, of 56 amniotic fluids judged to be either PG positive or weak positive, all but five had enzymatic PG concentrations greater than 1.5 mumol/l. The sensitivity of the A-FLM assay employed clinically for predicting foetal lung maturity was 89% and the specificity was 100%. The overall predictive accuracy of the test could be improved by providing controls at lower, more appropriate PG concentrations. Ninety-one fluids analysed by the A-FLM kit were subsequently tested for the presence of PG by two-dimensional thin-layer chromatography (2D TLC). A 94%-concordance between the methods was found.

Quantitative determination of phosphatidylglycerol in amniotic fluid by enzymatic assay.

Phosphatidylglycerol (PG) was extracted from 54 human amniotic fluids for the assessment of fetal lung maturity. The PG values were derived from an enzymatic assay involving initial conversion of PG to glycerol by phospholipase C and alkaline phosphatase with subsequent analysis of the glycerol formed. This method proved to be reliable when compared with a method for two-dimensional thin layer chromatographic (2D TLC) analysis of amniotic fluid phospholipids. The results revealed that in all but one of 27 amniotic fluids in which no PG was detected by 2D TLC, enzymatic PG concentrations were less than or equal to 1.5 mumol/l and out of these, from 10 newborn infants delivered within 72 h of sampling, 4 developed respiratory distress syndrome (RDS). Conversely, in all but one of 27 amniotic fluids found to contain PG by 2D TLC, enzymatic PG concentrations were greater than 1.5 mumol/l and except for one subject from non-identical twins, no infants developed RDS.

Direct gas chromatographic assay of urinary medium-chain fatty acylcarnitines by their thermal decomposition

We report a gas chromatographic assay for urinary medium-chain acylcarnitines which employs their property of thermal lability, and by circumventing the need for specialised mass spectroscopy is suitable for routine laboratory use. The method produces readily interpreted, uncomplicated chromatograms and has proved to be both sufficiently sensitive and specific to enable detection of octanoylcarnitine in a symptomatic individual with medium-chain CoA dehydrogenase deficiency and in two asymptomatic siblings following administration of a carnitine load.

Combined enzymatic assay of phosphatidylglycerol and phosphatidylcholine in amniotic fluid

We present here a combined, quantitative enzymatic procedure for determining amniotic fluid phosphatidylglycerol and phosphatidylcholine and relate these findings to the assessment of fetal lung maturity. Under the assay conditions described phospholipase C specifically hydrolyses phosphatidylglycerol (PG) and phosphatidylcholine (PC) but not sphingomyelin, precluding the need for removal of sphingomyelin prior to analysis. Solvent extraction of the phospholipids from the amniotic fluid is, however, employed to avoid spurious elevation of PG and PC results by endogenous glycerol and choline. Of 45 amniocentesis fluids examined, 28 yielded detectable PG concentrations (greater than 0.5 mumol/l) and all but three of these exhibited PC concentrations in excess of 10 mumol/l. One case of respiratory distress occurred in an infant of 29 wk gestation with severe intrauterine growth retardation. Of the remaining 17 fluids in which PG was undetected enzymatically (less than or equal to 0.5 mumol/l), 14 also contained PC concentrations less than or equal to 10 mumol/l and all six cases of true respiratory distress syndrome came from within this sub-group. Strong correlations between the PC concentration and the lecithin:sphingomyelin ratio, r = 0.85 (p less than 0.001) and the PC and PG concentrations, r = 0.96 (p less than 0.001) were also found.

Renal vein renin measurement and arteriography in the investigation and management of severe childhood hypertension

Forty-two children aged one to sixteen years with persistent and severe hypertension were investigated by renal vein renin measurements. There were no serious complications in the 49 procedures performed and technical failure occurred on three occasions. Arteriography was performed in 35. Asymmetrical renin release was found in 22 patients and of these 15 underwent surgery. This was successful in 12 patients (80%) who became normotensive. Ten had unilateral disease (100% cure rate) but only 2 (40%) with bilateral disease became normotensive. Renal vein renin studies combined with arteriography have a useful role in the investigation and management of childhood hypertension.

Investigation of Nithsdale goitre.

As a sequence to a survey which showed that the prevalence of goitre was higher in schoolchildren in Nithsdale (30%) than in Dumfries (16%), a total of 181 adult subjects from these 2 areas were examined and the plasma inorganic iodide concentrations (PII) were determined. The large majority of PII values in subjects from both areas were within the normal range and the overall conclusions are that iodine deficiency severe enough to account for a high prevalence of small goitre or a low prevalence of large goitre does not exist in the South West of Scotland. Since this area is likely to be representative of the U.K. in general, it is also concluded that there is no practical justification for general dietary iodine supplementation meanwhile.

Fetal maturity assessed from biochemical analysis of the liquor amini.

Two hundred and fifty-one samples of liquor amnii were analysed to determine the correlation between the biochemical constituents of the liquor and gestational maturity. Creatinine, oestriol and protein were the only constituents which, measured individually, correlated with maturity. The difference between the levels of creatinine in the amniotic fluid and maternal serum and the ratio of amniotic fluid to serum creatinine gave a lower percentage exact prediction than creatinine alone. Computing together all five parameters gave a prediction of gestational maturity to within 2 weeks in 73 per cent of cases. The biochemical content of the liquor amnii probably principally reflects maturation of fetal renal function, which does not necessarily correlate accurately with gestational maturity.